Methods are known for thermally polymerizing and copolymerizing dicyclopentadiene (DCPD) feedstocks and for hydrogenating the copolymer product. For example, U.S. Pat. No. 4,650,829 discloses a hydrogenated hydrocarbon resin having a softening point lower than 90.degree. C. and containing at least 40 weight % of monomer units derived from cyclopentadiene alone and cyclopentadiene plus a comonomer of the class consisting of alkyl-substituted cyclopentadiene, acyclic dienes, vinyl aromatics and mixtures thereof. U.S. Pat. No. 5,171,793 discloses the thermal polymerization of a vinyl aromatic component comprising a mixture of styrene and indene and alkylated derivatives thereof, and a cyclodiene at a temperature of 270.degree. C. for two hours. The dark colored resin product is mixed with a solvent diluent and hydrogenated to produce a resin having softening points higher than 100.degree. C. U.S. Pat. No. 3,040,009 discloses the production of light colored resins by redistilling the bottom fraction of dripolene, a normally liquid mixture of hydrocarbons obtained by high temperature pyrolysis of hydrocarbon gases. The thermally polymerized resin is hydrogenated using a catalyst consisting of metallic nickel distributed on a porous support.
In the past, the molecular weight of cyclopentadiene-based resins was controlled by including codimers of cyclopentadiene with a diene such as methylcyclopentadiene, butadiene, isoprene or piperylene, and also by adding these same linear dienes directly into the polymerization process. In these processes, insoluble waxy polymers were often obtained below a reaction temperature of 250.degree. C. Other methods of softening point and molecular weight control involved not only temperature, but also initial monomer concentration and time in the reactor. Advantages have also been claimed in the final adhesives when indene streams and/or C-9 streams are copolymerized with DCPD streams. However, these C-9 and indene streams are known to contain sulfur, which can create problems in the subsequent hydrogenation process due to early poisoning of the catalyst.
It is known that in a given family of hydrocarbon resins, i.e., all of those based on the same feedstock, as the softening point goes up, molecular weights and polydispersity also tend to increase. It is also known that there is a trend toward higher softening points and molecular weights as reaction times and temperatures are increased during the thermal homopolymerization of dicyclopentadiene. In addition, when vinyl monomers other than alpha-methylstyrenes are used to modify DCPD feedstocks, e.g., styrene and other ring-substituted styrenes such as t-butylstyrene and vinyltoluenes, high molecular weights and polydispersities result.
It would be desirable to provide thermally polymerized resins based on low cost DCPD feedstocks, with relatively low molecular weights and relatively high softening points that do not change substantially with time in the reactor. These resins should preferably readily convert to the corresponding hydrogenated water-white and thermally stable derivatives.